The invention relates to an apparatus for testing an immunity of various electric devices against electromagnetic interference and a method of testing and the immunity thereof, and more particularly to an apparatus and method for measuring and evaluating an immunity or a radio wave stress of various electric devices such as printed circuit boards, circuit elements and any electric and electronics devices as well as an apparatus for irradiating an electromagnetic wave or a radio wave for the immunity testing.
The value and importance of testing and measuring an immunity and electromagnetic wave stresses of any electronic devices such as digital circuits against various sources of electromagnetic wave interferences or radio wave interferences have been on the increase in view of electromagnetic environmental problems. These problems are serious problems on account of increase of an amount of irradiation of extra electromagnetic energies, typically excess radio noises. The concept of the electromagnetic environmental problems or electromagnetic compatibility had been established. The problem with radio noise interferences are serious. The radio noise may be defined as an electromagnetic wave which is able to be superimposed on an information signal, thereby causing an interference with any transmission of the informational signals. The device which may suffer the radio noise interference may include various electric and electronics devices involving, for example, printed circuit boards and cables. A radio noise which has entered into an electric or electronics device is able to cause a radio noise interference which places this device in an abnormal state, thereby resulting in various malfunctions of the device. Even if the electric or electronic device potentially possesses excellent performances, such device having suffered the radio noise interferences are no longer able to show such excellent performance.
From the above descriptions, the importance in establishing a useful technique for testing and measuring the immunity of the electric and electronics devices to the electromagnetic wave interference or the radio wave interferences could readily be appreciated.
One of the conventional techniques for testing the immunity of any electric and electronics devices to the radio noise interference is disclosed in September 1992 JEIDA-G10 second edition Chapter 3, pp. 4-5, "Guide Line for Immunity Test of Information Processing Equipment and System". The description will hereinafter focus on a structural explanation of the conventional immunity testing apparatus with reference to FIG. 1.
As illustrated in FIG. 1, the conventional radio wave immunity testing apparatus has an oscillator 5 for oscillating a frequency signal S. The conventional radio wave immunity testing apparatus also has an amplifier 7 being electrically connected to the oscillator 5 for fetching the frequency signal S for subsequent amplification of the fetched frequency signal S to generate a radio wave electrical signal P. The conventional radio wave immunity testing apparatus also has an antenna 8 being electrically connected to the amplifier 7 for fetching the radio wave electrical signal P to generate a testing radio wave R being usable for the electromagnetic stress test. The testing radio wave R is irradiated on a measuring sample 6 which is placed at a position of several meters from the antenna 8. The measuring sample 6 may be any electrical or electronics device having a tendency to suffer any impact due to the electromagnetic wave interference. The oscillator 5 is able to conduct an output control for controlling a level of the frequency signal S to be transmitted to the amplifier 7. The amplifier 7 is able to show a gain control for controlling a level of the radio wave electrical signal P to be transmitted to the antenna 8. The antenna 8 may be a large size and high gain bi-conical antenna or log-periodic antenna. The antenna 8 is adjustable in height for radiating a standardized radio wave R on the measuring sample 6 where the standardized radio wave R is a vertically or horizontally deflected radio wave having a standardized level in intensity of the electric field. The intensities in the electromagnetic fields may be classified into three levels as shown below.
TABLE I ______________________________________ Intensity of Intensity of Electric Field Magnetic Field Level (V/m) (dB micro-A/m) ______________________________________ 1 1 88.5 2 3 78.0 X Special 68.5 ______________________________________
TABLE 1 shows each level in the individual intensities of the electric and magnetic fields where the intensity of the magnetic field is calculated by converting the radio impedance 377 (ohm).
The above described electromagnetic stress test is accomplished within a large size electromagnetic environmental installation such as a radio wave darkroom capable of shielding any electromagnetic wave.
The above electromagnetic wave stress test may be implemented by evaluating whether the measuring sample 6 receiving the irradiation of the testing radio wave R shows a normal performance or an abnormal performance caused by the radio wave interference. When testing the immunity of a computer such as a personal computer, the testing radio wave R is irradiated on the computer which is executing a predetermined test program so as to evaluate whether the computer is able to correctly execute the test program or is unable to execute the test program to find any interruption of the execution of the test program due to the electromagnetic interference. When the measured sample 6 is any display device, the immunity ay be evaluated by irradiating the testing radio wave R on the display device as a measuring sample 6 so as to check any disturbance of a picture on a screen of the display device.
The above described immunity testing apparatus is able to test the electromagnetic wave stress test for a relatively large electric or electronics equipment, while another type of the immunity testing apparatus for measuring the electromagnetic wave stress of a relatively small measuring sample is disclosed in the above publication. The description thereof will be made with reference to FIG. 2.
As illustrated in FIG. 2, this other type of the conventional immunity testing apparatus has a TEM cell 9 in which the measuring sample 6 is accommodated. The TEM cell 9 comprises an enclosure member 92 and a central electrode 91, both of which are made of an electrically conductive material or such materials and further which must be separated electrically. The central electrode 91 is placed at the center position within the enclosure member 92. In FIG. 2, the enclosure member 92 and the central electrode 91 may serve as electrodes respectively so as to cause the transverse electromagnetic wave within the enclosure member 92 where the electric field E from the enclosure member 92 toward the central electrode 91 is illustrated. The measuring sample 6 placed in the enclosure member 92 of the TEM cell is then subjected to irradiation with the transverse electromagnetic wave (TEM wave) for the electromagnetic stress test for the measuring sample 6.
This other type of the immunity testing apparatus illustrated in FIG. 2 also includes a standardized signal generator 5 for generating a standardized signal. This other type of the immunity testing apparatus also includes an amplifier 7 being electrically connected at its input side to the standardized signal generator 5 for fetching the generated standardized signal from the standardized signal generator 5 for subsequent amplification of the standardized signal. The amplifier 7 is further electrically connected at its output side to one end of the enclosure member 92 in the TEM cell 9 so as to transmit the amplified signal to the enclosure member 92. The intensity of the electric field E is associated with the signal applied to the enclosure member 92. In the above, although the measuring sample 6 is accommodated in the enclosure member 92, the measuring sample 6 is required to be so placed as to be separated electrically not only from the central electrode 91 but also from the enclosure member 92 through an insulator. The enclosure member 92 in the TEM cell 9 has the opposite end at which the enclosure member 92 is electrically connected to a terminal 93 with an electrical resistance, for example, 50 ohm.
However, this conventional electromagnetic stress testing apparatus has problems as described below. In the conventional method for testing the immunity, the testing radio wave is irradiated on the entirety of the measuring sample 6. Hence, the above prior technique is unable to find or ascertain where an abnormal state appears within the measuring sample 6, even though it is able to confirm that the measuring sample 6 has been in the abnormal state. If the measuring sample device 6 is a personal computer, the conventional immunity testing apparatus is unable to determine the position where an abnormal operation appears. Namely, it is impossible for the prior art to confirm what element, for example, printed circuit boards accommodated in the personal computer body or an input-output key board or other element, is in an abnormal state. Accordingly, the conventional techniques for immunity test as illustrated in FIGS. 1 and 2 are merely able to ascertain that an abnormal state appears in at least one of the elements involved in the measuring sample 6, but would not be able to ascertain precisely what element involved in the measuring sample 6 has been in such an abnormal state.
Needless to say, it would, therefore, be very important to develop a novel method and apparatus for testing the immunity of any electric or electronics devices to confirm or ascertain precisely a position showing an abnormal operation within the measuring sample. Namely, it is required to provide novel immunity testing method and apparatus being able to ascertain precisely what element involved in the measuring sample 6 shows an abnormal operation or is in an abnormal state.
Moreover, techniques for antennas to be used in the immunity testing device would also be receiving a great deal of attention to realize an excellent and desirable immunity test for the electric and electronics device which tends to affect an impact of the interferences of the radio wave or the electromagnetic wave. Various types of antennas have been known in the art such as parabolic antennas and a loop antenna. It has been known in the art to use a loop antenna in place of parabolic antennas for applying locally an electromagnetic field on a part of a measuring sample.
An example of the loop antennas is disclosed in 1992 IEEE International Symposium On ELECTROMAGNETIC Comnpatibility pp. 439-442. As illustrated in FIG. 3, the loop antenna 61 is so positioned that a loop of the antenna faces in parallel to a surface of the measuring sample 6 at a distance of several centimeters. The above loop antenna has a diameter of several centimeters. In this case, the loop antenna is able to apply a magnetic field on a relatively small area on the surface of the measuring sample 6.
FIG. 4 illustrates a loop antenna 61 having a diameter of 16 millimeters where a magnetic field radiated from the loop antenna is measured by use of a probe. The probe is moved along the Y-axis for scanning wherein a distance between the loop of the antenna and the probe is 10 millimeters so that the probe may detect the magnetic field in a vertical component (Z-direction) and a horizontal component (X-direction). The probe may convert a variation of the detected magnetic field into a receiving voltage. FIG. 5 represents the result of the measurement of the magnetic field generated from the loop antenna 61 when the probe is moved along the Y-direction for scanning. In FIG. 5, a solid line represents a profile of receiving voltages corresponding to the vertical components of the measured magnetic field. Dotted lines represent profiles of receiving voltages corresponding to the horizontal components of the measured magnetic field. From FIG. 5, it could be understood that the vertical component of the measured magnetic field has a maximum value around a center position of the loop of the antenna 61. By contrast, the horizontal component of the measured magnetic field has a maximum value around diametrically opposite ends of the loop antenna. The maximum value of the vertical component of the measured magnetic field represented by the solid line is larger by about 6 dB than the maximum value of the horizontal component thereof represented by the dotted lines. This proves that the measuring sample 6 receives the magnetic field having not only the vertical composition but also the horizontal composition particularly around the diametrically opposite ends of the loop antenna. To realize the measurement of the electromagnetic stress of the measuring sample 6, it would, however, be required to apply a magnetic field having a vertical component only free of any horizontal component thereof. Particularly, the influence of the horizontal component of the magnetic field against the measurement of the electromagnetic stress of the measuring sample 6 may be considerable. When the loop antenna is used, it would be required according to the regulation to apply such a magnetic field as having any one of the vertical and horizontal components for a desired measurement of the electromagnetic stress of the measuring sample 6.
It would therefore be required to develop a novel antenna which permits a desirable local measurement of the electromagnetic stress test.